Process of cracking



2,782,145 PROCESS or CRACKING Seymour W. Ferris, Mount Holly, N. J., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application January 20, 1954, Serial No. 405,142

2 Claims. (Cl. 196-66) This invention relates to a process for treating heavy hydrocarbon oils, and pertains more particularly to a process for converting heavy petroleum residual fractions into lighter products.

An object of the invention is to provide a process for converting heavy petroleum oils, such as heavy residual fractions, into useful lower boiling materials. A further object is to provide a process for simultaneously converting a petroleum residual fraction and a petroleum paraffinic fraction to useful products such as gasoline, kerosene and clean cracking stock, without producing any significant quantities of coke. Other objects and their attainment in accordance with the invention appear hereinafter.

It has now been found that by simultaneously contacting (1) a heavy residual fraction heated to a temperature below that at which coke is formed, (2) an aromatic fraction heated to a relatively high temperature and (3) a heated paraffinic fraction, the contacting being performed under certain conditions of operation as hereinafter described, the residual fraction and the paraffinic fraction are converted to gasoline hydrocarbons and other useful products without concomitant coke formation.

According to the invention, a heavy hydrocarbon residual fraction is heated to a temperature below its cracking temperature, say about 700 F. The cracking temperature can be considered, for practical purposes, the same as the temperature of coke formation, and hence coke is not formed in this step. A refractory aromatic fraction, such as an aromatic hydrocarbon fraction consisting principally of benzene, is heated to a temperature above the cracking temperature of the residual fraction, say about 1150 F. A paraflinic fraction, such as a straight run fraction boiling from about 400 F. to 500 F. at atmospheric pressure, is heated to an elevated temperature preferably sufficient to cause incipient cracking thereof, say about 850 F. The three heated materials are then admixed, preferably substantially simultaneously, and the resulting reaction mixture separated into desired components. It has been found that in the process of the invention, the components of heavy residual fractions and of parafiinic fractions are simultaneously converted to lower boiling products without concomitant formation of significant quantities of coke.

It is preferred to admix the reaction mixture components substantially simultaneously, which means that the components are brought together at the same time within the limitations dictated by practical operation 01 the process. However, operation can be by admixing two components and shortly thereafter, prior to coke formation, introducing the third component into the admixture. When operating by this latter means, it is preferred to first admix the heated residual fraction and the heated parafiinic fraction, and then add the aromatic fraction heated to a relatively high temperature, or to admix the heated residual fraction and the aromatic fraction heated to a relatively high temperature, and then add the heated paraffinic fraction. It is always essential, regard- 2,782,145 Patented Feb. 19, 1957 less of the order of addition, that the three reaction mixture components be brought together before coke formation occurs. By using three fluid streams as described, full operational control is maintained by varying quantities of the reaction mixture components and the temperatures of each immediately prior to admixing. Also, in the instance where it is desired to heat the heavy residual fraction and the paraffinic fraction to the same temperature, the two fractions can be admixed prior to the heating and good results obtained.

The accompanying figure is a flow diagram illustrating the process of the invention, to which attention is now directed. A heavy residual fraction is introduced through line 1 and is heated in furnace 2 to an elevated temperature below that at which coke formation is observed, which temperature is also below its cracking temperature. An aromatic fraction is introduced through line 4 and is heated in furnace 5 to an elevated temperature below that at which it is decomposed but above the temperature at which the residual fraction is cracked. A paraffinic fraction is introduced through line 6 and is heated to incipient cracking in furnace 8. From the several furnaces, the heavy residual fraction, aromatic fraction and paraf-. finic fraction are passed through lines 9, 10, and 11, respectively, and are admixed in line 12. Reaction vessel 14 is preferably provided to insure adequate mixing and reaction time. If desired, an external source of heat can be supplied to vessel 14, especially if the residence time of the reaction mixture therein is appreciable. From reaction vessel 14 the reaction mixture passes through line 15 into fractionator 16, in which the reaction products are separated. Low boiling materials such as normally gaseous hydrocarbons which may be formed in the reaction are removed through line 18. A fraction corresponding substantially in boiling range with the aromatic fraction introduced through line 4 is removed through line 19. The aromatics are removed from other materials such as saturates by means known to the art, such as by silica gel adsorption, in separator 20. The aromatic fraction is recycled through lines 21 and 22. When desirable or necessary, such as when aromatics within the desired range are produced in the process, all or a portion of the aromatic fraction can be removed from the process through line 24. The saturates separated from the aromatics are removed through line 25. Other products, such as fractions boiling within the gasoline, kerosene and diesel fuel ranges are recovered such as through lines 26, 28 and 29, it being understood that other fractions, as desired, can be recovered by the fractionation. For example, the relatively high boiling distillate products are excellent charge stocks for catalytic cracking operations. Also, a parafiinic fraction corresponding to the reaction mixture component introduced through line 6 can be recovered from the fractionator and recycled to the process. Unconverted or insutficiently converted heavy residual hydrocarbons are removed through line 30 and recycled to the process through line 31. If desired, all or a portion of this residue can be discarded through line 32.

The heavy residual fractions which can be employed in the process are the relatively high boiling petroleum fractions such as residue from the distillation of crude oil. Other processes which form suitable heavy residual fractions, or hydrocarbon mixtures from which the heavy residual fractions can be obtained include, for example, catalytic cracking, thermal cracking, reforming polymerization, hydrogenation, destructive hydrogenation, and the like. Such residual fractions are generally highly aromatic in character, and are known to be rapidly converted to coke on heating to a temperature sufficient for cracking. The fractions usually boil above 600 F. at atmospheric pressure.

The temperature to which the residual fraction should ice be heated prior to admixing with the other reaction mixture components varies with the properties of the fraction being used. In general, the temperature of the residual fraction immediately prior to "admixing with the other reaction components should be as high as possible without causing coke formation, In practice, this temperature will usually be from about 650 F. to 900 F., but lower or higher temperature, can be used, and may be required, with specific residual stocks.

Aromatic fractions which can be employed are hydrocarbon fractions composed principally of refractory aromatics, i. e. aromatic hydrocarbons which are not converted at the temperatures employed in the present process. Refractory aromatic hydrocarbons that can be employed include, for example, benzene, toluene, the xylenes, the trimethyl benzenes, naphthalene, methylnaphthalene, the dimethylnaphthalenes, and mixtures thereof. These hydrocarbons are inert when heated to the relatively high temperatures required by the process.

The temperature to which the aromatic fraction should be heated depends upon the conditions of the specific reaction. In general, the aromatic fraction should be heated to a temperature sufficient to raise the temperature of the residual fraction, on admixing, to a value above its cracking temperature, as hereinafter described. The temperature to which the aromatic fraction should be heated will usually be within the range of from about 1000 F. to 1300" F., but lower or higher temperatures can be used, and may be required in specific instances.

The paraffinic fractions which can be employed are the petroleum hydrocarbon fractions which are composed principally of saturated hydrocarbons, and which boil above about 130 F. It is preferred, however, toemploy a petroleum naphtha having a boiling range above about 300 R, such as a straight run petroleum fraction boiling substantially within the range of from about 375 to 500 F. It is also preferred to employ a paraffinic fraction having a boiling range above the boiling range of the aromatic fraction. Olefins are less effective than paraffins in preventing coke formation, and hence should not be present to an extent of more than about Aromatic hydrocrabons, however, can be present in substantial amounts without deleteriously affecting the process. As much as 35% by volume of the paraffinic naphtha may be composed of hydrocarbons having an aromatic ring, but preferably the quantity thereof is not greater than about by volume. Saturated hydrocarbons, including paraffins and naphthenes, are the principal constituents of the paraffinic fractions that give good results.

The temperature of the parafiinic fraction immediately prior to admixing with the other components of the process should be such that the temperature of the resulting admixture is above the cracking temperature of the residual fraction and the cracking temperature of the paraffinic fraction. Preferably the temperature of the paraffinic fraction, prior to admixing, is sufficient to achieve incipient cracking thereof, i. e. to achieve a small amount of cracking. In most operations the temperature will be from about 675 to 950 F.

In carrying out the process of the invention it is preferred to mix the three reaction mixture components substantially simultaneously, such as by continuously combining fiowing fluid streams of the components, as above described. The quantities of the three components can be varied within the limits given hereinafter. It is essential, however, that the quantities and temperatures of the three components be such that the temperature of the admixture be above that required to crack the residual fraction.

The quantity of paraffinic fraction can be varied substantially and good results obtained. In general the quantity to employ should be maintained within the weight ratio thereof to residual fraction of from 0.321 to 3:1. It is not desired to be limited by theoretical ,con-

siderations, but it is believed that the parafiinic fraction, preferably heated to incipient cracking, supplies radicals which react with the aromatic radicals from the cracking of the heavy residual fraction. By combining in this manner, the aromatic radicals are prevented from reacting with each other to form highly condensed aromatic materials and subsequently coke. It is also believed that, at the temperature employed, the paraffiuic portion of the so-formed materials is cleaved to form smaller radicals which can unite further with aromatic radicals from the residual fraction. In this manner a single saturated hydrocarbon from the parafrinic fraction can ultimately react with, and prevent coke formation from, a multiplicity of radicals from the heavy residual fraction.

The quantity of aromatic fraction to employ depends upon the specific materials being reacted and the temperatures thereof on admixing. The quantity must be such that the temperature of the reaction mixture is above the cracking temperature of the residual fraction. Of course, when heating the aromatic fraction to a relatively high temperature prior to admixing, a smaller quantity can be employed than when it is heated to a lower temperature. The quantity of aromatic fraction will also depend upon the quantity and temperature of the paraflinic fraction employed. In general, the weight ratio of aromatic fraction to residual fraction plus paraffinic naphtha will be. from about 0.5 :1 to 10:1.

The reaction mixture components are maintained substantially in liquid phase during heating thereof, and except for relatively low molecular weight hydrocarbon gases which may be formed in the process, the reaction mixture prior to fractionation is maintained substantially in the liquid phase.

The following specific embodiment illustrates the process of the invention. About gallons per hour of a heavy residual fraction from the thermal cracking of gas Oil, consisting principally of condensed aromatic hydrocarbons, is simultaneously admixed with 100 gallons per hour of benzene and 75 gallons per hour of a parafiinic naphtha, which was a 400-500 F. straight run petroleum fraction containing 18 volume percent aromatic hydrocarbons, the remainder being saturate hydrocarbons including paraflins and naphthenes. Immediately prior to admixing, the residual fraction is heated to about 700 F., at which temperature practically no coke or cracking is observed, the benzene is heated to about 1150" F., and the paratfinic naphtha to about 825 F., at which temperature incipient cracking, i. e.. a small amount of cracking is observed. The temperature ofthe resulting admixture, about 875 F., is sufficient to cause substantial cracking of the residual fraction. On fractionation of the reaction mixture, desired fractions are recovered, such as gasoline, kerosene, diesel fuel and the like. Relatively high boiling distillate fractions form good cracking stock. Gasoline and kerosene fractions are recoverable in especially good yields.

It is essential to the successful operation of the process of the invention that a residual fraction heated to below its cracking temperature be contacted with an aromatic fraction in the presence of a paraffiuic fraction under conditions of operation whereby the temperature of the residual fraction is raised above its cracking temperature, as above described. Variations within the broad scope of the invention can be made, such as the use of catalysts. In some instances cracking catalysts such as silicaalumina, silica-girconia, and the like, which may be compounded with metals or metallic oxides such as molybdenum oxide and chromium oxide, can advantageously be employed. It is preferred to contact the reaction mixture .with the catalyst immediately after admixing the components of the reaction mixture, or to admix the reaction mixture components in the presence of the catalyst.

Another preferred embodiment of .value when it is desired to introduce a parafiinic fraction into the reaction mixture at a temperature below incipient cracking thereof is to contact the paraflinic fraction with a cracking catalyst immediately prior to its introduction into the reaction mixture, so that incipient cracking is readily achieved.

The invention claimed is:

1. Process for simultaneously converting a heavy petroleum residual fraction and a petroleum straight run paratfinic naphtha to lower boiling hydrocarbons which comprises: (a) heating a heavy petroleum residual fraction, maintained in the liquid phase, to a temperature which is below its cracking temperature and which is within the range of from about 650 to 900 F.; (b)

heating a refractory aromatic fraction composed principally of aromatic hydrocarbons selected from the group consisting of benzene, toluene, the xylenes, ethylbenzene, naphthalene, and mixtures thereof, maintained in the liquid phase, to a temperature within the range of from 1000 to 1300 F.; (c) heating a straight run petroleum paraifinic naphtha boiling within the range of from 375 to 500 F., maintained in the liquid phase, to the temperature at which incipient cracking occurs and which is within the range of from 675 to 950 F.; substantially simultaneously admixing liquid streams of the three soheated materials at rates such that the temperature of the resulting admixture is above the cracking temperature of the residual fraction and the paraifinic naphtha, whereby a portion of said residual fraction and a portion of said paraflinic naphtha are converted to lower boiling hydrocarbons without concomitant coke formation, and

separating said lower boiling hydrocarbons from the reaction mixture.

2. Process for simultaneously converting a heavy petroleum residual fraction and a petroleum straight run parafiinic naphtha to lower boiling hydrocarbons which comprises: (a) heating a heavy petroleum residual fraction, maintained in the liquid phase, to a temperature which is below its cracking temperature and which is within the range of from about 650 to 900 F.; (b) heating a refractory aromatic fraction, maintained in the liquid phase, to a temperature within the range of from 1000 to 1300 F.; (c) heating a straight run petroleum paraflinic naphtha boiling above about F., maintained in the liquid phase, to the temperature at which incipient cracking occurs and which is within the range of from 675 to 950 F.; substantially simultaneously admixing liquid streams of the three so-heated materials at rates such that the temperature of the resulting admixture is above the cracking temperature of the residual fraction and the parathnic naphtha, whereby a portion of said residual fraction and a portion of said parafiinic naphtha are converted to lower boiling hydrocarbons without concomitant coke formation, and separating said lower boiling hydrocarbons from the reaction mixture.

References Cited in the file of this patent UNITED STATES PATENTS 1,817,672 Butler Aug. 4, '1931 2,377,613 Conn June 5, 1945 2,626,892 McCulley et a1 Jan. 27, 1953 

2. PROCESS FOR SIMULTANEOUSLY CONVERTING A HEAVY PETROLEUM RESIDUAL FRACTION AND A PETROLEUM STRAIGHT RUN PARAFFINIC NAPHTHA TO LOWER BOILING HYDROCARBONS WHICH COMPRISES: (A) HEATING A HEAVY PETROLEUM RESIDUAL FRACTION, MAINTAINED IN THE LIQUID PHASE, TO A TEMPERATURE WHICH IS BELOW ITS CRACKING TEMPERATURE AND WHICH IS WITHIN THE RANGE OF FOR ABOUT 650 TO 900*F., (B) HEATING A REFRACTORY AROMATIC FRACTION, MAINTAINED IN THE LIQUID PHASE, TO A TEMPERATURE WITHIN THE RANGE OF FROM 1000 TO 1300*F.; (C) HEATING A STRAIGHT RUN PETROLEUM PARAFFINIC NAPHTHA BOILING ABOVE ABOUT 130*F., MAINTAINED IN THE LIQUID PHASE, TO THE TEMPERATURE AT WHICH INCIPIENT CRACKING OCCURS AND WHICH IS WITHIN THE RANGEOF FROM 675 TO 950*F.; SUBSTANTIALLY SIMULTANEOUSLY ADMIXING LIQUID STREAMS OF THE THREE SO-HEATED MATERIALS AT RATES SUCH THAT THE TEMPERATURE OF THE RESULTING ADMIXTURE IS ABOVE THE CRACKING TEMPERATURE OF THE RESIDUAL FRACTION AND THE PARAFFINIC NAPHTHA, WHEREBY A PORTION OF SAID RESIDUAL FRACTION AND A PORTION OF SAID PARAFFINE NAPHTHA ARE CONVERTED TO LOWER BOILING HYDROCARBONS WITHOUT CONCOMIFANT COKE FORMATION, AND SEPARATING SAID LOWER BOILING HYDROCARBONS FROM THE REACTION MIXTURE. 